Ability to use and set variables for use in text everywhere - including tool tips, shape text, and text boxes. When printing or exporting, the *values* of each variable should be given.

[kblum007]

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Is your feature request related to a problem? Please describe.
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I have many utility functions that each show up in a many places in my diagrams. I list parameter types in the shape, and description of the function in the tooltip. If the function changes, it's very time consuming and frustrating to update all of them.

Describe the solution you'd like
Ideally, I'd like to define the variables in the diagram tab, perhaps as a set/array of name-value pairs that I can use on any page within the diagram. The variables should be easily referenced within text (e.g. ###variable-name###). To (1) facilitate the switch between the variable and the realized value and (2) let the user know when a variable has not been defined, the Text tab of Format should have variable options similar to:
(1) Show variable names, which would hide the value and allow the variable to be removed or changed. Deselecting this option would show the value instead.
(2) Highlight variables (with two highlight color options), which would highlight the variable name or the value (whichever one is visible), using one highlight color for names and the other for values.

Describe alternatives you've considered
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Additional context
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